Mercury interrupter



Patented Dec. 24, 1940 UNITED STATES PATENT OFFICE MERCURY INTERRUPTER assignor to Detroit, Mich., a

Application November 19, 1938, Serial No. 241,384

4 Claims.

This invention relates to circuit interrupters and more specically to means for automatically periodically interrupting current flow for changing current or voltage characteristics in direct current circuits.

There are of course many instances in which it is desired to operate devices from a direct current source which require different voltage or current than that available, or perhaps may require a pulsating uni-directional current -instead of a constant direct current ilow. One illustration of such a condition or plurality of conditions occurs in automotive vehicles where i it is necessary to supply many accessories such as clocks or radios with -power from the storage battery having a given potential or perhaps to provide power for some of the essential operating parts of the vehicle from said same battery such as, for example, the fuel pump in which instance it is necessary to provide a pulsating current.

It is a basic fact that we cannot change the voltage or current ratio of direct current. We can, however, by interrupting such a current obtain a pulsating direct current which we can use in many instances exactly as we use alternating current and it is for all practical purposes a one-half wave alternating current. With this pulsating current we may change the current and voltage ratios as desired. These, of course, are known facts and various means have been developed for periodically interrupting or breaking the current from a direct current source, one of the better known devices being a vibrator such as is used for power supply in an automotive radio receiving set. These devices however utilize mechanical movement andare therefore subject to deterioration both of the switch points and the mechanical vibrating structure.

It is therefore an object of my invention to provide means for automatically interrupting a direct current to provide a more flexible pulsating direct current for any use.

It is a further object of my invention to provide such a current interrupter as shall be substantially insensitive to deterioration and have long life. f

Itis a further object of my invention to provide such a current interrupter as shall be very simple in construction and relatively easy to manufacture and use.

When a certain material isutilized as a conductor of electric current, if this material is changed from one physical condition toy another it frequently ceases to be a conductor, at least at the particular potential applied, and' therefore the circuit is broken.

I have found through experimentation that if there is placed in contact with a pool of mercui-y a material having higher resistance than (Cl. o-113) mercury, and a suicient amount of current passed through the two bodies'in series, that a heating eiect will occur and a change in physical condition will result and the how of current cease. The mercury in this instance is heated at the juncture of the two bodies, vaporizes and causes a short cessation of a series circuit. This Will cause the heating to cease, the mercury vapor condenses and reestablishes a contact between the mercury and higher resistance member and current will again ow to provide heat, causing a recycle.

It is believed that the operation Ijust described is due to the following reasons after some study, but it is to be understood that these may not include all of the actions or reactions taking place. In this instance the relatively small amount of mercury in series is that exactly in contact with the end of the higher resistance member. Thus as the mercury in contact with this tip or point has current passed therethrough, it is heated, vaporizes and breaks the circuit. It of course immediately condenses to complete the circuit again and We have a duplication of the operation. We are able to control the operation due to design of the tip and area which controls the operation of the interrupter.

With the above explanation and objects in mind, my invention will be better understood by reference to the following specification and claims and illustrations in the accompanying drawing, in which:

Figure 1 is a vertical section through one form of interrupter embodying my invention.

Figure 2 is a vertical section through another form showing a modification of my invention.

As stated above, the primary purpose of my invention is to provide some mechanical support so that broadly there is contact between a pool of mercury and a small surface area of a member having substantially higher resistivity to the passage of electrical current than mercury, both of these being in a series circuit. One material which may be mentioned as an example is carbon. There are of course many varied forms of accomplishing such a result and those shown here are only examples of a very small portion of the physical forms that my device may take.

Referring particularly to Figure 1, there is shown therein an outer glass envelope 2 within which is suspended an inner glass envelope 4 having sealed therein a small carbon mass 6, said mass being entirely surrounded by glass except at the lowermost portion where a small area such as 8 projects through an opening in the glass envelope 4. The space between the inner glass envelope 4 and outer envelope 2 is substantially iilled by a pool of mercury I0 and there is provided one electrode I2 which extends down into the mercury pool III and a second electrode I4 which is staked into the carbon or other high resistant mass 6. The only requisite of the mercury contact between the area 8 and mercury bath is that there shall always be a sufficient amount of mercury to allow passage of the currentand this particular design has been devised so that the interrupter will operate in substantially any position and it is shown in dotted lines on its side where it operates satisfactorily.

In the operation of this device current passes through the electrode I4 and into the high resistant mass 6, is concentrated through the area 8 and passes into the mercury pool I0 and out again through the electrode I2. Where the surface 8 contacts the mercury I0 the current ls so concentrated as to cause a relatively high degree of heating which vaporizes the mercury in contact therewith to cause circuit interruption which as stated previously immediately condenses and recycles so that we have an automatic circuit interrupter.

It may be pointed out at this point that this is inherently a low voltage device for if we apply such a voltage as will sustain an arc through mercury vapor the circuit will not break after the vapor has once been formed. We have found Afrom experimentation that the highest voltage upon which this will operate and give satisfactory results as an interrupter is approximately I4 volts.

Referring now to Figure 2 which operates in exactly the same manner, but which is a slightly diierent form, we have there an outer shell 20 formed of glass or other insulating material and a second concentric inner glass shell 22 supported therein. Within the lower portion of the inner shell 22 there is supported a mass 24 of high resistant material similar to that shown at 6 in Figure 1 which fills the lower extremity of the shell 22 and as before protrudes as shown at 26 through a small opening 28 in the lower tip of the member 22. There is a small opening 30 provided in the side Wall of the shell 22 and mercury such as 32 is shown filling the lower half of .the outer portion between shell 22 and 20 and a second smaller pool of mercury 34 within the shell 22, the opening 30 being provided so that mercury may flow back and forth. An electrode 36 is staked down through the center of the shell 22 but stops short of the upper surface of the high resistant material 24, contact between the two being provided by the mercury 34. A second electrode 38 is supported at any point so that it may contact the mercuryv bath 32. This device operates in exactly the same way as that shown in Figure 1 but in view of the construction it is necessary to operate this type only in the upright position shown; otherwise there will be gaps in the circuit.

Therefore the essential features of my design are a shell for supporting a. bath of mercury and an electrode insulated from the shell and having higher electrical resistance than mercury which presents adenite area for current flow. Only sufficient insulation is required to maintain a series circuit through the electrode and mercury bath. It is of course obvious that as the amount of current that it is desired to control is increased, the area of the tip will have to be altered in proportion. It has been found that porous carbon pendent gives better results than too hard a carbon be- -cause a certain amount of the mercury is absorbed in the pores of the tip and gives more satisfactory vaporization in combination with the mercury actually in contact with said tip. i

While this interrupter is substantially insensitive to frequency, that is, it will operate at any frequency depending upon the external circuit to which it is connected, there are certain factors which slightly affect its own frequency characteristics and these are as follows: 1. Mercury pressure withinv the shell which is influenced by the height of the mercury column. 2. By the operating temperature of the mercury. 3. By the diameter of the point or tip exposed to the mercury (as the area increases the frequency increases).

Starting current of the device initially is also a function of point area and therefore it is seen that by proper design of point area one can control within limits starting current and to some extent the frequency although it is always to be remembered that this device is inherently deonly on the external circuit for its frequency characteristics and will operate on the frequency determined by the characteristics of the circuit in which it is connected.

I claim:

1. In a circuit interrupter, a shell, a second shell within the first and spaced therefrom, a pool of mercury partially filling the space between the two shells, a member of higher electrical resistivity than mercury supported within the inner shell, a portion projecting therethrough to contact'the mercury and means for applying a potential difference to the member and mercury in series.

2. In a circuit interrupter, a shell, a second shell supported within the first and spaced therefrom, a carbon member supported within the inn-er shell, said last-named shell having an opening, a substantially small tip of the carbon member projecting through the opening, mercury partially filling the space between the inner and outer shells and means for applying a potential to the mercury and the carbon member whereby theA current flow will be concentrated at the carbon tip and mercury contact causing vaporization at this point and current interruption.

3.' In a circuit interrupter, a unitary member of insulating material forming two hollow shells, one Within the other, a blocll:V of material of comparatively high electrical resistivity supported within the inner shell having a small portion projecting through an opening therein and a body of mercury occupying the space between the inner and outer shells whereby it will contact the portion of the block which projects through the inner shell and means connected to both the block and the mercury to apply a potential difference thereto.

4. In a circuit interrupter, a pair of glass bulbs, one within the other and forming a. unitary assembly, a pool of mercury in the space between the two bulbs and a carbon electrode rigidly molded within the inner bulb and projecting through a small opening therein to contact the mercury pool and electrodes supported by the assembly to apply a potential difference to the mercury and carbon electrode in series.

' WILLIAM S. BRIAN. 

